I'm sorry to hear about this with Ruan. We need to determine if he's regurgitating or, instead, vomiting.
A bird that bobs its head up and down in a sort of pumping motion, beak open and then a purposeful delivery of partially digested food is regurgitating. This is something they would do to feed offspring or a mate. It’s done by some birds to objects (toys, mirrors, people) they are particularly fond of - especially if they’re in a breeding season, when a bird wants to please their owner and/or is of a nervous temperament. Regurgitation that is unusual enough for you to make note of it like you have, might be a symptom of crop infection/impaction/”sour crop”.
Vomiting is more of a head “flicking” event. The bird will often seem uneasy, pacing or uncomfortable and although the head bobbing might be similar to the regurgitation action, it’s usually more of a shaking and the end result is a very splattered, sticky substance that may or may not include food. When there’s blood showing in the vomitus it may indicate esophageal or proventricular ulcers.
An avian vet (please see here: theparrotsocietyuk.org/veterinaryadvice/avian-vets) will take a look into your bird’s mouth as part of a thorough physical examination and is likely to examine a swab of the oral cavity for abnormal numbers of either bacteria, yeast, or parasites. A good exam will also check for changes in the mucous membranes as seen with hypovitaminosis A (a lack of vitamin A in the diet) ulcers, and tumors.
Vomiting is a more serious symptom and seeing a vet as soon as possible is important. Gram-negative bacterial infections are commonly found and often caused by poor sanitation while food handling but there are far too many possible diseases to list here and as in any case of illness, getting it evaluated, diagnosed and treated promptly is best. I would be more comfortable knowing that Ruan was examined by an avian vet.
If Ruan won't drink and eat on his own please consider sweet potato, carrot, or squash baby food on a spoon tapped and dabbed on the underside of his upper beak. Show him where the rest of the baby food can be found. Please heat up his environment to 29.4C so Ruan need not expend excess energy keeping his body temperature up.
Nutritional imbalances are a common cause of illness in our pet birds. What has Ruan's diet consisted of, please? Seeds should comprise less than 20% of his diet. A diet of mainly seed and nuts has excessive fat, carbohydrates, and phosphorus; marginal protein; adequate vitamin E, and are deficient in amino acids, calcium, available phosphorus, sodium, manganese, zinc, iron, vitamins A, D3 (necessary for efficient absorption of calcium), K, and B12, riboflavin, pantothenic acid, choline, and available niacin. Ideally, a balanced pelleted diet such as can be found here: www.harrisonsbirdfoods.com or here: www.lafeber.com/pet-birds should be fed as well as hard-boiled egg yolk, pancakes and cornbread, the tops of fresh greens, dairy products such as yogurt and cheese - yes these low lactose foods are safe, fresh fruits such as apples, pears, melon, kiwi, and berries, vegetables such as broccoli, carrots, beets, asparagus, cabbage, sweet potato, and squash, and even tiny pieces of meat.
Please respond with further questions or concerns if you wish.